The aims of the research are 1) to document the relationship between menstrual cycle patterns of female hormones and reproductive behavior of chimpanzees and 2) to determine whether oral contraceptives (OCs) have adverse effects on the behavior patterns. Oppositely sexed pairs of chimpanzees will be tested behaviorally during natural cycles (control) and during cycles with OC administration, using two different test paradigms under each condition. Urine will be collected from the female for hormone assay to facilitate interpretation of results in terms of the hormonal regulation of behavior. In one paradigm, the female is confined with the male in a single cage, with little opportunity for choice regarding mating. In the second paradigm, the female must work (lever press) to gain access to the male. The two paradigms, previously used successfully with gorillas and orang-utans, permit assessment of different components of male and female behavior, contributing to a comprehensive evaluation of hormone-behavior relationships during natural cycles and cycles with OC administration. The data from natural cycles will complete our comparative studies of endocrine correlates of reproductive behavior in the great apes. Because of the endocrine and behavioral similarities between the chimpanzee and human, the results related to OC administration should have implications for humans with sexual problems, where use of OCs is thought to contribute to the etiology of the problems. The results with OCs may also provide us with an acceptable method for experimentally manipulating hormone levels of intact females, necessary for investigating cause and effect relationships (as contrasted with correlations) between hormones and behavior.